Each File Upload Data telecommand packet contains up to 52 bytes of actual file data. The file data is extracted sequentially from the original source file and inserted into consecutive upload-telecommand packets.

The sequence flags, sequence count, and checksum must be valid for every upload telecommand packet; otherwise, an error is generated. In the event of an error, not only is the current upload packet discarded, but the entire file upload is invalidated. As each CCSDS upload packet is received and validated, the file data contents contained in that packet are extracted and copied to the appropriate offset within the RAM file upload buffer. From there, the file contents may copied to the storage device with a File Upload Commit command.

The example below shows the construction of an upload transfer of N packets. The 'SF' marker shows the value of the CCSDS packet header sequence flags. The 'SC' marker shows the value of the CCSDS packet header sequence counter. The sequence count in the first packet of the upload is designated 'S'. The sequence count must increment predictably from the value presented in the first packet.